I think Shrink spells should absolutely be a thing for stealth and accessing areas in games with magic, though I know that's easier said than done depending on the game.
I've made my own magic for Skyrim before, and there's engine-nonsense that gets in the way of it working how one would expect. Specifically, the "hit box" of both the player and non-player characters don't resize with the player model unless reloaded.
Put a less nerdy way, if a six foot tall person were to shrink to one feet tall, and someone threw a basketball four feet above their shrunken head, it would hit them. They would also cover the same amount of ground when walking or running, and would continue to effectively function as though not shrunk until they entered a new area or something.
THAT SAID, if we're holding the games industry to the standards of Skyrim, we're holding those standards too low (I love ya, Skyrim, but you know I'm right), and being able to shrink to move more quietly, be less visible, and access new areas is just fun, and could naturally come with defense and speed debuffs that would make it a trade-off to use. I think that's more interesting than a simple invisibility spell, in any case.